The present invention relates to a liquid crystal device and manufacturing method for the same.
In recent years, ferroelectric liquid crystal materials have attracted the interest of researchers due to their quasi-hysteresis characteristics. The performance of this type liquid crystal device depends largely on the distance between a pair of substrates in which liquid crystal material is disposed. If there is substantial disparity in distance between the substrates, the response times of respective constituent cell elements are dispersed, and degradation of display performance and irregular color result.
The disparity is produced mainly during the filing process of liquid crystal material in the narrow space between the substrates. Vacuum filling method is a known method for filling the space between a pair of substrates of a liquid crystal device with a liquid crystal to manufacture a liquid crystal device. In this prior art method, the liquid crystal device is entered in a vacuum chamber at a vacuum together with the liquid crystal material followed by evacuation of the chamber to a vacuum condition, and then, after the inlet port of the device is caused to sink in the liquid crystal, the pressure is elevated to an atmospheric pressure so that the liquid crystal enters the liquid crystal device through the inlet port. One type of this method is described in Japanese application No. sho 60-175192.
However, there are several shortcomings associated with this method. The inlet port of the liquid crystal device is substantially narrow so that the pressure in the liquid crystal device can not be lowered rapidly. Because of this, the liquid crystal device is subjected to the differential pressure between the inside and the outside of the liquid crystal device and deformed due to the pressure when the vacuum chamber is evacuated, and therefore the thickness of the liquid crystal layer necessarily becomes nonuniform.
To comply with the shortcoming, it is proposed to mate a pair of substrates firmly to bear the differential pressure and maintain the distance between substrates by making use of hard spacers disposed therein. However, since the filling of liquid crystal material is carried out at an elevated temperature, there are formed void spaces or fissure-like branching defects when the temperature is descended to room temperature.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a liquid crystal device in which a liquid crystal layer is formed with a constant thickness.
It is another object of the present invention to provide a method of manufacturing liquid crystal devices without causing the occurrence of branching defects in a liquid crystal layer formed between the pair of substrates.
The above and other objects and advantages are accomplished by designing appropriate configuration of the spacers distribution. Through a number of experiments, an essential factor which contributes to uniformity of the distance between the substrates has been found. The factor is the ratio of the distance between the substrate before the filing of liquid crystal material to the distance after the filing. In case of ferroelectric liquid crystals, the ratio has to be chosen to be from 0.77 to 0.87 in order to obtain minimum disparity in thickness of the liquid crystal layer between the substrate.